The invention relates to an electrical heating element with an insulated housing particularly in the form of a heating cartridge for heating liquid media such as water, oil or the like, particularly for use or incorporation in water heaters such as continuous flow heaters, coffee percolators, washing machines or the like with a duct system connecting an inlet with an outlet for the medium to be heated which flows over uninsulated heating coils within the duct system.
Heating cartridges of this type are, for example, known from DT-AS 1,106,004 corresponding to German Utility Model 1,810,419 and substantially comprise a parallelepiped-shaped cast resin member, within which the water and therefore heating ducts are juxtaposed in the form of cavities extending substantially in the longitudinal direction of the cartridge. To obtain an adequate duct length, the ducts are arranged to and fro. The duct system is produced by drilling blind holes from one narrow side of the parallelepiped. This narrow side is sealed by a locked cover plate and interposed insulation. On the opposite side are provided both an inlet and an outlet for the water. Electrical contact terminals are also provided on the said narrow side of the parallelepiped.
Although heating cartridges of this type have relatively high heating powers up to about 10 to 12 kW, their main disadvantages consist of a relatively complicated construction making it almost impossible to replace the heating coil when it burns out and the costly combersome manufacture, particularly of the duct system. Since the construction of the parallelepiped in one piece prevents the removal from an injection mould or conventional mould into which the ducts would have to be moulded, too, the ducts have to be drilled. Thus, three blind holes have to be drilled in the longitudinal direction of the parallelepiped, the two outer holes having the same diameter whilst the central hole has a larger diameter. This central hole is divided by a plug-in panel. The insertion of the heating coil into the thus produced duct system requires a great deal of skill and special tools so as not to damage the heating conductor windings during insertion. Furthermore, at the reversal points, the heating conductor must be stretched and bent which additionally stresses it and due to its close engagement with the wall, it can easily burn into the wall. As the removal of the heating conductor requires above average skill, its replacement and repair become substantially impossible, i.e. it is only possible to replace the complete heating cartridge. It must be borne in mind that with such heating cartridges, it is relatively easy for the heating coil to burn through if, for example, for any operational reason the water flow is interrupted and simultaneously the switch for the supply of power remains connected. Furthermore, through the drilling of the heating ducts, angles remain at the deflection points in which liquid can build up and bubbles of air can be deposited, which particularly with a low water pressure or low throughput, could easily lead to the annealing and burning out of the heavily loaded heating coil. Finally, after drilling, the ducts must be very carefully cleaned because any drillings remaining can either lead to obstructions in the liquid flow or to the scorching and therefore to an easier burning out of the heating conductor.